Nicotiana tabacum produces several different pyridine alkaloids, with nicotine representing the most abundant. The alkaloids that accumulate to a lesser degree include anatabine, nornicotine, myosmine, and anabasine. These alkaloids are commonly referred to as minor alkaloids. Minor alkaloids are direct precursors in the formation of tobacco specific nitrosamines.
Nitrosamines and in particular, tobacco specific nitrosamines (TSNAs) are constituents of tobacco. Anatabine, a minor alkaloid, is nitrosated to form N′-nitrosoanatabine (NAT). NAT constitutes approximately 40% of total TSNAs. The biosynthesis of anatabine, and its associated genes, is not completely known. However, current understanding is that the synthesis of anatabine requires quinolinate phosphoribosyltransferease (QPT), a key enzyme regulating entry to the pyridine nucleotide cycle.
Biosynthesis of anatabine is thought to proceed via the conversion of nicotinic acid to 3,6-dihydronicotinic acid. After decarboxylation to produce 3,6-dihydropyridine, and condensation with nicotinic acid to produce an intermediate, conversion to anatabine can occur by dehydrogenation. The current understanding of the alkaloid biosynthetic pathway is depicted in FIG. 1.
In addition to TSNAs, certain polyphenol compounds can form undesirable phenolic compounds during the combustion of tobacco and may also be targeted constituents of tobacco smoke. There is interest in providing a method for reducing the contents of these targeted compounds in tobacco.